1. Field of the Invention
The present invention relates to a process for growing a GaAs monocrystal film suitable for forming a monocrystal growing layer of GaAs in the order of a single molecular layer.
2. Description of the Prior Art
In the past, as a gas phase epitaxy technique for obtaining a film crystal of a semiconductor, an organic metal gas-phase growing process (hereinafter called "MO-CVD process")and a molecular beam epitaxy process (hereinafter called "MBE process") have been known. However, where a compound semiconductor between III-group to V-group as in GaAs is grown by the MOCVD process, III-group and V-group elements as a source with a hydrogen gas as a carrier are simultaneously introduce for growth thereof by thermal cracking, and therefore the grown layer is poor in quality. There is a further disadvantage in that the order of the single molecular layer is difficult to control.
On the other hand, the MBE process well known as a crystal growing process which utilizes a super-high vacuum employs physical adsorption as a first stage, and therefore, the quality of crystal obtained thereby is inferior to the gas-phase growing process which utilizes chemical reaction. When a compound semiconductor between III-group - V-group as in GaAs is grown, IIIgroup and V-group elements are used as a source, the source itself being installed within a growing chamber. Because of this, controlling the emitted gas obtained by heating the source and the amount of vaporization, and supplying the source are difficult to do, and it is difficult to maintain the growth rate constant for a long period of time. Furthermore, a vacuum device such as discharge of vaporized material becomes complicated. Moreover, it is difficult to precisely control the stoichiometry of the compound semiconductor, and after all, there poses a disadvantage in that a crystal of high quality may not be obtained.
In view of the foregoing, the present inventors have previously proposed a semiconductor crystal growing process having a controllability of a grown film layer of the single molecular layer order (see Japanese Patent Application Nos. 153977/1984 and 153978/1984 Specifications). This will be explained with reference to FIG. 5.
In FIG. 5, reference numeral 1 designates a growth chamber, which is formed of metal such as stainless steel; 2, a gate valve; 3, an exhaust chamber for making the growth chamber 1 super-high vacuum; 4, 5, nozzles for introducing gaseous compounds of component elements of III-group and V-group of III-group - V-group compound semiconductors, for example; 6, 7, valves for opening and closing the nozzles 4, 5; 8, a gaseous compound containing a component element of III-group; 9, a gaseous compound containing a component element of V-group; and 10, a heater for heating the base, which is a tungsten (W) wire with quartz glass sealed therein, the wire or the like not shown. Reference numeral 11 designates a thermocouple for measuring the temperature; 12, a base for a compound semiconductor; and 13, a pressure gauge for measuring vacuum within the growth chamber.
The process for the epitaxial growth of GaAs molecular layers one by one on the base 12 is accomplished in the following procedure. That is, the e 2 is opened, and the interior of the growth chamber is evacuated to the extent of 10.sup.-7 to 10.sup.-8 Pascal (hereinafter merely indicated at Pa) by the superhigh vacuum evacuation device 3. Next, the GaAs base 12 is heated by means of the heater 10 to the extent of 300.degree. to 800.degree. C., and the valve 6 is opened to introduce TMG (trimethylgallium) 8 as a gas containing Ga into the tank for 0.5 to 10 seconds in the range that pressure within the growth chamber is from 10.sup.-1 to 10.sup.-7 Pa. Thereafter, after the valve 6 is closed to evacuate the gas within the growth chamber 1, the valve 7 is opened to introduce AsH.sub.3 (arsine) 9 as a gas containing As into the chamber for 2 to 200 seconds in the range that pressure is 10.sup.-1 to 10 Pa. Thereby, at least one molecular layer of GaAs may be grown on the base 12. The aforementioned steps of operation are repeated to successively grow single molecular layers, whereby the epitaxial grown layer of GaAs having the desired thickness may be grown with accuracy of a single molecular layer.
Incidentally, when in the process of crystal growth, the temperature of the crystal growth is increased, vacancies, atoms between lattices and the like are to present. In addition, impurities become taken in due to autodoping or the like, which is not preferable in view of growing crystals of high completeness. To avoid this, it is necessary to grow crystals without increasing the temperature. However, according to the previously proposed crystal growing process, the crystal growing temperature is relatively high, from 300.degree. to 800.degree. C., thus failing to obtain a single crystal of GaAs having a high completeness.